Respiratory muscle weakness and chest wall abnormalities in neuromuscular diseases (NMD) may lead to decreased pulmonary volumes. We assessed the reversibility of vital capacity (VC) reduction with mechanical In-Exsufflation (MI-E). We evaluated the effects of positive inspiratory and negative expiratory pressures on spirometric variables under passive (without patients' participation) and active (with active participation) application in 47 NMD patients. VC, inspiratory capacity (IC), expiratory reserve volume (ERV) were measured during maneuvers without and with MI-E assistance, delivering inspiratory assistance (+40cmH2O), expiratory assistance (-40cmH2O) and both (±40cmH2O). Passive and active assistance improved significantly VC and IC compared to baseline (P